A conventional gas turbine installed as an aircraft engine typically comprises a compressor for compressing ambient air, a combustor for burning fuel together with compressed air, and a turbine for converting the expanding air from the compressor/combustor to usable power. In operation, the gas turbine is driven by expanding combustion gases. These combustion gases also drive a fan component which is connected to the turbine in order to produce thrust used for propelling, for example, an air craft, As known to those skilled in the art, a compressor is a key component of any gas turbine, as it typically consumes roughly sixty percent (60%) of the energy needed to produce the resulting torque or thrust. As a result, management of compressor efficiency is a key consideration for any gas turbine operator.
Gas turbines engines consume large quantities of air. Air contains foreign particles including, for example, aerosols and solids. These foreign particles enter gas turbine compressors when gas turbine engines are running. The majority of the foreign particles will follow the gas path and exit a turbine engine together with exhaust gases. Other types of air contaminants, such as those found in an aerodrome environment, include pollen, insects, engine exhaust, leaking engine oil, hydrocarbons coming from industrial activities, salt coming from nearby sea, chemicals coming from aircraft de-icing and airport ground material such as dust.
After a period of operation of an aircraft gas turbine engine, a coating of these foreign particles and/or contaminants tends to builds up in engine's compressor. This build-up is also known as compressor fouling. As known to those skilled in the art, compressor fouling causes a change in the properties of the boundary layer air stream of the engine's components. In addition, the compressor fouling increases the compressor's surface roughness.
A turbofan engine is designed for providing a high thrust level for use in aircrafts operating at subsonic velocities. As a result, turbofan engines are widely used in commercial passenger aircraft applications. Typically, turbofan engines comprise a fan and a core engine. The fan is installed upstream of the engine's compressor, and consists of one rotor disc with rotor blades and alternatively, a set of stator vanes downstream of the rotor. The fan is driven by the power from the core engine. The core engine is a gas turbine engine designed such that power for driving the fan is taken from a core engine shaft. While the engine is running, prime air enters the fan.
As discussed above with regard to gas turbine compressors, the fan of a turbofan engine is also susceptible to fouling caused by air contaminants/particles such as insects, pollen, birds, etc. This fan fouling is typically removed by washing using cold or hot water only. As known to those in the art, cleaning fan fouling is a relatively easy process to perform.
As noted above, in a turbofan engine, downstream of the fan is the core engine compressor. Significant for the compressor is its ability to compress air to high pressure ratios. In performing its compression work, the compressor will experience a temperature rise. The temperature rise in a high pressure compressor may be as high as five-hundred (500) degrees Celsius. As a result of these high temperatures, any fouling that collects on the compressor is effectively “baked” onto the surface of the compressor, making it extremely difficult to remove.
Analyses have shown that compressor fouling comprising hydrocarbons, residues from anti icing fluids, salt, and/or the like are more difficult to remove than other types of fouling.
In an effort to remove engine compressor fouling, a number of cleaning or washing techniques have been developed. For example, one such compressor cleaning system is disclosed in International Publication No. WO 05077554, titled “Method and Apparatus for Cleaning Turbofan Gas Turbine Engines” and its corresponding United States Published Patent Application No 2006/0048796. Disclosed therein is a cleaning device comprising a plurality of nozzles arranged on a stiff manifold, which manifold is releasibly mounted on the air inlet of the engine, and where the nozzles are arranged to atomize and direct cleaning liquid in the air stream up-stream of a fan of the engine.
The device as disclosed in WO 05077554 comprises a first nozzle arranged at a first position relative a centre line of the engine such that the cleaning liquid emanated from the first nozzle impinges the surfaces of the blades substantially on the pressure side; a second nozzle arranged at a second position relative the centre line of the engine such that the cleaning liquid emanated from the second nozzle impinges the surfaces of the blades substantially on the suction side; and a third nozzle arranged at a third position relative the centre line of the engine such that the cleaning liquid emanated from the third nozzle passes substantially between the blades and enters an inlet of the core engine. A specific design washing configuration is prepared for each specific engine and flow rate such that atomization and nozzle position are optimized to achieve effective cleaning.
Thus, the invention disclosed in WO 05077554 is based on the insight that the engine geometry and properties of the fouling of different components of the engine have different properties and therefore, require different approaches for the cleaning. As an example, the fouling of a core compressor may have different properties than fouling found on the blades of a fan. One possible reason for this discrepancy in fouling properties may include, for example, that the temperature is much higher at the compressor than at the blades of a fan. The high temperature at the compressor results in fouling particles becoming “baked” onto the compressor's surface, thereby making removal of such fouling extremely difficult. At the fan blades, however, the temperature is much lower. As a result, the fouling at the fan does not become baked, making it much easier to clean fan fouling.
The cleaning solution disclosed in WO 05077554 provides several advantages over the existing solutions. One advantage is that each engine part is cleaned according to the particular properties of the fouling collected thereon. To illustrate, since the fouling collected on a compressor is usually baked on and thus, much more difficult to remove than say, fouling that gathers on the blades of a fan, the cleaning process each of these components may be adapted accordingly. As a result, the engine as a whole (i.e., the entirety of the engine parts exposed to fouling) may be cleaned more effectively and efficiently as compared to conventional engine cleaning methods, which typically utilize a uniform cleaning process for cleaning all engine parts. To this end, this device provides each engine component with a specific washing nozzle design, configuration, and optimized washing procedure that is selected in order to maximize the effectiveness/efficiency of the overall engine wash procedure.
Another aspect of the cleaning aircraft engines includes the proper collection and disposal of washing liquids used to clean the engines, and any contaminants removed from the engines during a cleaning process. Due to environmental concerns, used washing liquids may be purified and recycled, such as is described in International Publication No. WO 05120953, titled “System and Devices for Collecting and Treating Waste Water from Engine Washing”. Disclosed therein is a device having a collector arranged at the rear arrangement for engine washing. Waste wash liquid emanating from an engine is collected by this collecting device at the rear of the engine.
Another example of a waste water collecting device is described in International Publication No. WO 05121509, titled “System and Devices for Collecting and Treating Waste Water from Engine Washing”, and its corresponding United States Published Patent Application No. 2006/0081521. As disclosed therein, collected waste liquid is pumped into a tank where released fouling material is separated from the collected liquid by an appropriate waste water treatment process. The treated water is then used for either washing additional engines or is alternatively dumped into a sewer.
The above mentioned systems for cleaning engines and/or collecting and recycling used washing liquids provide very versatile and effective cleaning methods that can be arranged on a mobile unit. These processes, however, are all dependent to some extent upon an operator manually making certain adjustments and/or system settings.
When an aircraft engine is to be washed, for example, an operator is provided with information regarding the engine type and collects a manifold that is adapted to that engine from a storage place. When in position at the aircraft, the manifold is attached to the inlet of the engine and connected to the washing system. The operator is further provided with information regarding the requirements for washing that particular engine type, such as maximum water flow per time unit and the total amount of washing water. The operator then manually sets the valves to the manifold nozzles in order to obtain the appropriate pressure and flow and keeps track of the washing time.
Since this part of the washing operation is done manually there is always a risk that the human factor jeopardizes the result, and in particular since many engine washing operations are performed during night-time when the operators may not be fully alert. If the requirements regarding the particular engine are not followed, the engine may be damaged, leading to a very costly standstill of the aircraft or that the result of the washing procedure is inferior, whereby the benefits of an engine wash are not obtained.
It would therefore be beneficial for such a closed loop washing process if the influence of the human factor is minimized as much as possible.